Threshing machines of the type described herein are often used to separate the stem of a leaf from the lamina portions of the leaf. Preferably, the stem should be separated from the rest of the leaf with a minimum of damage to the lamina and providing the largest possible lamina pieces. The above process is generally executed using a series of threshing machines in which the first machines have a rotor which rotates relatively slowly and has relatively widely spaced teeth radially extending from the rotor which are effective to tear the largest pieces of lamina from the leaf stem. The separated pieces of lamina and remaining feedstock pass through relatively large openings of a semicircular screen or basket which is beneath and in close proximity to the ends of the threshing teeth. The separated pieces of lamina and remaining feedstock are then conveyed to a separating machine. The larger lamina pieces which are lighter than the remaining heavier feedstock are separated from the feedstock and collected. The remaining portions of the leaf together with its stem then pass to a successive threshing stage in which the threshing rotor rotates at a slightly greater velocity and has a greater number of threshing teeth extending radially therefrom with lesser spaces between the teeth. Further, the openings in the screen or basket are smaller. This stage of threshing is effective to remove smaller pieces of lamina from the leaf stem which are conveyed to a downstream separator stage in which the loose smaller pieces of lamina are separated from the remaining stem and collected. The processes of threshing, separating and collecting successively smaller pieces of lamina are repeated with successive threshing machine stages each having a threshing rotor rotating successively faster and having a successively greater number of more closely spaced, radially extending threshing teeth.
Threshing machines of the above type may have threshing rotors that range in length from three feet to twelve feet. Further, the threshing rotors may have a center body which is up to sixteen inches in diameter, and threshing teeth may radially extend from the center body an additional five inches. The larger threshing rotors may weigh up to two tons. There are basically two designs for connecting the radially extending threshing teeth to the threshing rotor. With the first, or fixed tooth position design, parallel pairs of ears are welded to the outer cylindrical surface of the center body of the thresher rotor. The threshing teeth are inserted between the welded mounting ears and are held in place by a bolt which extends through the mounting ears and the threshing tooth in a direction that is generally parallel to the longitudinal axis of the threshing rotor. Consequently, the tooth has a degree of freedom, that is, it can rotate or pivot about the mounting bolt in a plane perpendicular to the longitudinal axis of the threshing rotor. To prevent that rotation, one of two mechanisms may be used.
The first mechanism requires that a keystock such as a small rectangular bar be welded to an edge of the mounting ears adjacent both of the longitudinal edges of the threshing tooth so that the welded keystocks prevent the threshing tooth from pivoting in the plane perpendicular to the axis of the threshing rotor and support the threshing tooth in the desired radial direction with respect to the threshing rotor. However, if, in the threshing process, the tooth encounters a hard object; and an excessive force is applied to the threshing tooth in a direction opposite the direction of angular rotation of the threshing rotor, the keystock supporting the tooth which is subject to that excessive force will break away thereby permitting the threshing tooth to rotate about the mounting bolt. The break-away action of the keystock protects the threshing tooth and threshing rotor and the adjacent basket from excessive damage.
Another mechanism for preventing the threshing tooth from pivoting about the mounting bolt and holding the threshing tooth in the generally radial direction is to provide a notch in the outermost ends of the mounting ears, and to locate a shear pin that extends through the threshing tooth in those notches. Consequently, if the threshing tooth is subjected to an excessive force in opposition to the direction of the rotation of the threshing rotor, the shear pin will break. Therefore, the shear pin prevents excessive damage to the threshing tooth, the threshing rotor and the basket.
Threshing rotors of the above fixed tooth position design have an advantage in that damaged threshing teeth may be easily replaced because each tooth is individually secured into place with a very accessible mounting bolt. However, the mounting ears for the threshing teeth are welded in place on the threshing rotor, and, therefore, the relative positions of the threshing teeth are fixed. Consequently, the design has the disadvantage of being inflexible in rearranging the threshing teeth in different patterns. Further, in order to remove and insert the mounting bolt through the mounting ears there must be a predetermined clearance space between adjacent sets of mounting ears. Consequently, the design has a disadvantage in limiting the density of threshing teeth on the threshing rotor. The above limitations on the placement and density of threshing teeth limits the applications of the above-described fixed tooth position threshing rotor. For example, the fixed tooth position threshing rotor may be used in the first and sometimes second threshing stages, but is generally not applicable to a third and subsequent threshing stages.
To overcome the disadvantages of the fixed tooth position threshing rotor, the disc-type threshing rotor was developed. With this design, the threshing rotor is comprised of a plurality of adjacent ring-like rotor discs which slide over and are stacked together on a cylindrical center body. Each rotor disc has a plurality, for example, six, threshing teethmounting locations. The mounting locations are defined by an equal number of circumferentially spaced holes close to the outer periphery of the rotor disc. The rotor discs are mounted on the center body so that all of the holes are in longitudinal and axial alignment with respect to the thresher rotor. Any pattern of threshing teeth may be achieved by placing the threshing teeth at selected mounting locations between the rotor discs. There are six circumferential threshing tooth locations on each threshing disc; and further, with the 0.25 inch thick rotor discs being separated by a spacing therebetween of 0.25 inches, threshing teeth may be located at any 0.500 inch increment over the length of the threshing rotor. The essentially no practical limitation on the spacing between threshing teeth or the pattern in which the threshing teeth are arranged.
The threshing teeth are pivotally held in position by rods that extend through mounting holes in all of the threshing discs. The ends of the rods are secured against the end plates which in turn are connected to end shafts. As described, with respect to the fixed tooth position threshing rotor, the threshing teeth can be held and supported in a generally radial direction by a pair of keystocks welded on one side of the rotor disc at each of the tooth mounting locations. Consequently, by locating the threshing teeth between pairs of welded keystocks, the threshing teeth are supported and held in the desired radially orientation. As described above, if an excessive force is applied to the edge of the threshing tooth in a direction opposite the direction of rotation of the threshing rotor, that excessive force will fracture and break the keystock receiving the force. Therefore, the threshing tooth is permitted to pivotally rotate about the mounting shaft thereby protecting it and the threshing rotor from excessive damage.
While the above disc-type threshing rotor design provides practically infinite flexibility in the placement of threshing teeth, the replacement of damaged threshing teeth and broken keystocks is substantially more difficult. As will be appreciated, welding a new keystock in its proper location within the 0.250 inch spacing between adjacent rotor discs is very difficult. Alternatively, disassembly of the rotor to replace broken keystrokes is difficult, time consuming and expensive. Consequently, under the pressures of production, instead of replacing the broken keystock, a new or existing threshing tooth is often welded to an adjoining rotor disc.
The above disc-type rotor design may also utilize the shear pintype of construction in which notches are cut into the outer peripheral edge of each of the rotor discs adjacent the mounting holes. Therefore, rotor teeth having shear pins inserted therein are disposed between the rotor discs and the shear pin is located in the peripheral notches. Once again, an excessive force on the shearing tooth will shear the pin and permit the shearing tooth to pivot with respect to the mounting shaft. While the shear pin design with the disc-type roller has the advantages of a practically infinite flexibility with regard to placement of the threshing teeth, and further eliminates the problems associated with replacing keystocks, the design has proven to have the disadvantage of being susceptible to too frequent breakage of the shearing pin. The shear pin design is further complicated because spacing washers are used between the rotor discs at those tooth mounting locations where no teeth are mounted. Therefore, to replace a broken shear pin or threshing tooth, when the threshing tooth mounting shafts is removed and reinserted, spacing washers, shear pins and threshing teeth must be handled and maintained in alignment.
Both the keystock and shear pins designs have a further disadvantage in that when they absorb the energy of an excessive force and break, pieces of metal are separated from the threshing rotor. Those pieces could lodge and wedge within the rotor assembly; they could find their way into and damage other mechanical components or they could enter the feedstock and require separation. In any event, it is undesirable for the threshing rotor components to break into separate pieces.